Coloring oxide coated aluminum and product



United States Patent 3,057,761 (IOLGRING OXIDE COATED ALUMINUM AND PRGDUCT Henry J. Wittroclr, Opportunity, Waslr, assignor to Kaiser Aluminum & Chemical Corporation, Oakland, Calif., a corporation of Delaware No Drawing. Filed llday 9, 1960, Ser. No. 27,481 22 Claims. (Cl. 148-61) This invention relates to the production of colored coatings on aluminum and aluminum base alloys. More particularly, thisinvention relates to the coloring of oxide coatings on aluminum and aluminum base alloys characterized by stability in natural sunlight or ultra-violet light, and to the articles produced thereby.

For many purposes aluminum surfaces are protected by an oxide coating produced on the surface either by chemical treatment or by exposure as an anode in an electrolyte capable of yielding oxygen on electrolysis. The operation of forming such coatings electrolytically is commonly termed anodizing and the aluminum surface thus protected commonly termed anodized. Such treatments generally provide colorless, grayish layers of oxide coating on aluminum. It has long been desired to color such oxide coated aluminum surfaces. In the past, such colored surfaces have been produced by first anodizing or chemically treating the aluminum metal base and thereafter, dyeing the oxide coating with organic dyes. Such processes possess certain inherent disadvantages with regard to color stability in natural sunlight or under ultraviolet light in that the colors tend to fade rapidly when exposed under such conditions.

This invention comprises immersing oxide coated aluminum metal in a Warm aqueous solution of a salt of aurintricarboxylic acid selected from the group consisting of the sodium, potassium and ammonium salts, after which it is immersed in a warm aqueous solution of a salt having the general formula MX, where M is a metal selected from the group consisting of chromium, copper and cobalt, and X is an anion selected from the group consisting of sulfates, acetates, chlorides and nitrates. Next, the aluminum metal is immersed in a sulfuric acid solution and again immersed in a warm aqueous solution of a salt of aurintricarboxylic acid selected from the group consisting of the sodium, potassium and ammonium salts. If desired, the first immersion in the aqueoiw solution of the salt of aun'ntricarboxylic acid may be eliminated in some instances and a colored alumi num metal surface With good light stability may be produced. Further, good light stability and color may be achieved in some instances if the intermediate step of immersion in a Warm aqueous salt solution having the general formula MX is eliminated or if the immersion in sulfuric acid is eliminated. However, immersion in either the salt solution having the general formula MX or the sulfuric acid is essential and for superior results with regard to light stability and color in general, it is preferred to include all the above recited steps. In some instances, further improvements with regard to light stability may be obtained by immersion of the metal in a pretreatment solution prior to the first immersion in the salt of aurintricarboxylic acid. For this pretreatment, it is preferred to employ an aqueous solution of ammonium bifluoride and nitric acid. Additional suitable pretreatment solutions include an aqueous 5% sulfuric acid solution and an aqueous 5% phosphoric acid solution.

Depending on the lustre or brightness of the colored aluminum metal desired, that is the degree of specular reflectance, the aluminum metal may be subjected to various treatments prior to anodizing For example, where high lustre or brightness is desired, the base metal aqueous solution of sulfuric gram of salt per liter 3,057,761 Patented Oct. 9, 1962 may be subjected to conventional polishing or brightening treatments, e.g. mechanical, chemical or electrochemical. Where it is desired that the ultimate article have a matte or satin appearance, the base metal may be subjected to a suitable etching treatment. An example of a satisfactory procedure embodying the principles of this invention is set forth below, it being understood that the conventional water rinsing operations after the various steps are not recited.

(1) Clean metal in an inhibited alkaline cleaner.

(2) (a) Where high lustre or brightness of the ultimate colored composite is desired, treat metal according to a suitable bright dip process.

(b) Where a matte appearance is desired in the ultimate composite, subject material to a caustic etch treatment in a solution of 5% sodium hydroxide plus 2% sodium fluoride maintained at a temperature 0f'160 F. for a 5-minute immersion period.

(3) Produce a porous oxide coating by oxidation of the surface layer of the aluminum by chemical or electrochemical means such as by chemical conversion or by anodizing. For example, anodize for 1 to 120 minutes in an electrolyte consisting essentially of an aqueous solution of from 5% to 30% sulfuric acid maintained at a temperature of from 30 to 100 F. The current density may range from about 5 to 30 a.s.f. and the voltages may range from about 0 to 30 volts. As used herein, the term a.s.f. is an abbreviation or contraction of the expression amperes per square foot.

(4) Immerse for from 5 seconds to 2 minutes in an aqueous solution of from 2 to 100 grams per liter of a salt of aurintricarboxylic acid selected from the group consisting of the sodium, potassium and ammonium salts having a pH of from 3 to 8, and a temperature of from 120 to 185 F.

(5) Immerse for from 2 to 7 minutes in an aqueous solution of one of the following salts: chromium sulfate, chromium acetate, chromium chloride, chromium nitrate, copper sulfate, copper acetate, copper chloride, copper nitrate, cobalt sulfate, cobalt acetate, cobalt chloride and cobalt nitrate. The concentration should range from 1 of water to saturation and the solution should have a pH of from 1 to 4 and a temperature of from 120-160 F.

(6) Rinse for from 15 seconds to 5 minutes in an acid having a concentration of from .05 to .5% by Weight H a pH of from 1 to 3, and a temperature ranging from room temperature 70 F.) to 150 F.

(7) Immerse for from 2 to 10 minutes in an aqueous solution of from 2 to grams per liter of a salt of aurintricarboxylic acid selected from the group consisting of the sodium, potassium and ammonium salts hav 8 and a temperature of from to 185 F.

(8) The oxide coatings may be sealed by a conventional sealing treatment, e.g., immersion in hot water maintained at a temperature of from to 200 F. and a pH of from 5-6 for a period of from 10 to 30 minutes. The aluminum metal should then be rised in distilled water and dried.

In order to establish the superior light fastness of the colored anodic oxide coatings produced in accordance with this invention and the composite article coated therewith over those produced by conventional prior art methods, [tests described hereinbelow have been conducted.

In these tests, samples were fabricated from sheets of aluminum alloys 5357 and '1100 cut into 1" by 3" rectangles providing a total surface area of about 6 square inches per sample. The 5357 alloy samples had the following composition in percent by weight: silicon 0.08, iron 0.11, copper 0.01, manganese 0.28, magnesium 1.00,

f 3,057,761 q q a 3 4 zinc 0.01, titanium 0.02, balance aluminum. The 1100 ous solution of sulfuric acid contained in a 1 liter beaker. alloy samples were commercially pure aluminum contain- Samples 1-3 and 6 were immersed 15 seconds in a .05% ingaminimum of 99% aluminum. by weight aqueous sulfuric acid solution having a pH In these tests the samples were treated as indicated of 3 at room temperature. Sample number was imbelow, it being understood that the conventional cold 5 mersed for five minutes ina.5% by weight aqueous solu- Water rinsing operations after the various steps are not tion of sulfuric acid having a pH of 2 and a temperarecited: ture of 150 F. Step number 7 was not employed with (1) All samples were cleaned to a water-break free sample number 4. surface in a mild inhibited alkaline cleaner of the type (8) All samples were immersed for 5 minutes in an containing a mixture of carbonates, phosphates and sili- 10 aqueous solution of a salt of aurintricarboxylic acid as incates maintained at 160 F. Samples '1l4 were etched dicated in the table having a concentration of 10 grams for five minutes in an aqueous solution of 5% sodium of salt per liter of water. This solution was maintained hydroxide and 2% sodium fluoride at a temperature of at a pH of 5 and at a temperature of 150 F. and was 160 F. Samples and 16 were bright dipped in a contained inalliterbeaker. solution containing 80.3% by weight H PO 3.8% by 15 (9) All samples were sealed by immersion in boiling weight HNO balance water maintained at a temperature distilled water for 10 minutes, rinsed in distilled water of about 200 F. for a period of about 2 minutes. and dried.

(2) Samples 1-14 were rinsed for 15 seconds in 50% All the samples treated as above described were charby volume nitric acid at room temperature. acterized by a red color having a pleasing appearance.

(3) All samples were anodized in a 50 gallon rec- 20 The superiority of the method of this invention is tangular tank equipped with stirring devices and lead clearly demonstrated by a comparison of the dye life of cathodes for 30 minutes with direct current in an aqueous samples 1-6 and 15 employing the method of this insulfuric acid electrolyte containing 15% by weight VentiOIl With S p and 16 employing a Single H 30 at a temperature of 70 F. The current density dy ing treatment without either of the intermediate steps was maintained at 12 a.s.f. In general, the voltages 6 and 7. Dye life Was determined by measuring diffuse necessary to maintain a given current density vary with reflectance whereby a gain in diffuse reflectance indicates the cell and the anodizing conditions and the required g- A g in diffuse reflectance is pp voltage varies as the anodizing progresses. In anodizing mately the maximum permissible for commercial acthe samples employed in these tests, the voltages required ceptability. Each sample was subjected to ultra-violet to maintain a constant current density of 12 a.s.f. ranged lig t in a testing box and the number of hours in such from about2to 17 volt test box required for a 25% gain in diffuse reflectance (4) Sample 6 was immersed for ten econd in a room determined. The number of hours for each sample is temperature (70 F.) aqueous pretreatment solution conin i a d in the tabl For good light stability it is taining 25 g./l. NH HF 15 ml./l. HNO (70%), baldesirable to have a dye life greater than 300 hours. It ance water. The solution was contained in a 1 liter 05 Will be Seen from the table that Of the Samples beaker. -l4 and 16 employing the prior art method has a dye (5) Samples of 1-6 and 15 were imrnsersed i a aquelife as great as 300 hours and many of these samples had ous solution of the salt of aurintricarboxylic acid india very short dye life. However, samples 1-6 and :15

cated in the table having a concentration of 10 grams all had a dye life greater than 300 hours thereby demonof salt per liter of water for a period of one minute. strating the superiority of the method of this invention In the table aurmtrrcarboxylic acid is indicated by A.T.C. and the articles produced thereby.

Table Step5 Ste 6 Ste 8 Sample No. Alloy Salt of p Salt? of Dye A.T.O. A.'I.C. Life Salt g./l. pH

CI2(SO4): 7.3 1.5 NH 400 CuSO 10 4.5 NH; 510 01101, 10 4.1 N114 410 {oosoi 10 g lllfmsoi 2 1 9 370 NHr 500 CF2(SO4)5 7.3 1.5 NH; 740 NH; 160 NH; 100 N114 190 Na 150 Na I NH4 80 NH; NH, 100 CI(CgH302)3 5 l 5 Na 410 K 70 The solution was contained in a 1 liter beaker. The pH As used herein, the term aluminum is meant to cover of the solution was 5 and the temperature was 150 high purity aluminum, commercial purity aluminum and (6) Samples 1-4, 6 and 15 were immersed for five aluminum alloys. minutes in an aqueous solution of a salt having the gen- It will be understood that various changes, omissions eral formula where M is a metal selected from and additions may be made to this invention without dethe group consisting of chromium, copper and cobalt, parting from the spirit and scope thereof as set forth in and where X is an anion selected from the group conthe appended claims. srsting of sulfates, nitrates, acetates and chlorides. This What is claimed is:

solution was containedin a 1 liter beaker. The salt em- 1. In the art of coloring oxide coatings on aluminum ployed, the concentration in grams of salt per liter of metal, the improvement comprising the steps of immersing water and pH are indicated in the table. The solution the oxide coated aluminum metal in an aqueous solution Was maintained at a temperature of 150 F. Step numof a salt of aurintricarboxylic acid selected from the group her 6 was not employed with sample No. 5. consisting of the sodium, potassium and ammonium salts,

(7) Samples 13, 5 and 6 were immersed in an aqueimmersing the so-treated aluminum metal in an aqueous solution of a salt having the general formula MX, wherein M is a metal selected from the group consisting of chromium, copper and cobalt, and X is an anion selected from the group consisting of sulfates, acetates, chlorides and nitrates, followed by immersion in an aqueous solution of sulfuric acid, and immersing the aluminum metal for a second time in an aqueous solution of a salt of aurintricarboxylic acid selected from the group consisting of the sodium, potassium and ammonium salts.

2. The method of claim 1 wherein the oxide coated aluminum metal is immersed in a pretreatment solution prior to the first immersion in the salt of aurintricarboxylic acid.

3. The method of claim 2 wherein said pretreatment solution is an aqueous solution of ammonium bifluoride and nitric acid.

4. In the art of coloring oxide coatings on aluminum metal, the improvement comprising the steps of immersing the oxide coated aluminum metal in an aqueous solution of a salt of aurintricarboxylic acid selected from the group consisting of the sodium, potassium and ammonium salts, immersing the so-treated aluminum metal in an aqueous solution of sulfuric acid followed by a second immersion of the aluminum metal in an aqueous solution of a salt of aurintricarboxylic acid selected from the group consisting of the sodium, potassium and annnonium salts.

5. In the art of coloring oxide coatings on aluminum metal, the improvement comprising the steps of immersing the oxide coated aluminum metal in an aqueous solution of a salt having the general formula MX, wherein M is a metal selected from the group consisting of chromium, copper and cobalt, and X is an anion selected from the group consisting of sulfates, acetates, chlorides and nitrates, immersing the so-treated aluminum metal in an aqueous solution of sulfuric acid and finally immersing the aluminum metal in an aqueous solution of a salt of aurintricarboxylic acid selected from the group consisting of the sodium, potassium and ammonium salts.

6. In the art of coloring oxide coatings on aluminum metal, the improvement comprising the steps of immersing the oxide coated aluminum metal in an aqueous solution of a salt of aurintricarboxylic acid selected from the group consisting of the sodium, potassium and ammonium salts, immersing the so-treated aluminum metal in an aqueous solution of a salt having the general formula MX, wherein M is a metal selected from the group consisting of chromium, copper and cobalt, and X is an anion selected from the group consisting of sulfates, acetates, chlorides and nitrates, and finally immersing the aluminum metal for a second time in an aqueous solution of a salt of aurintricarboxylic acid selected from the group consisting of the sodium, potassium and ammonium salts.

7. In the art of coloring anodic oxide coatings on aluminum metal, the improvement comprising the steps of immersing the oxide coated aluminum metal for from seconds to 2 minutes in an aqueous solution of from 2 to 100 grams per liter of a salt of aurintricarboxylic acid selected from the group consisting of the sodium, potassium and ammonium salts having a pH of from 3 to 8 and a temperature of from 120 to 185 F., immersing the sotreated aluminum metal for from 2 to 7 minutes in an aqueous solution of a salt having the general formula MX, wherein M is a metal selected from the group consisting of chromium, copper and cobalt and X is an anion selected from the group consisting of sulfates, acetates, chlorides and nitrates, said salt being in a concentration ranging from 1 gram of salt per liter of water to saturation having a pH of from 1 to 4 and a temperature from 120 to 160 F., followed by immersion of the aluminum metal for from seconds to 5 minutes in an aqueous solution of from .05 to .5% by weight sulfuric acid having a pH of from 1 to 3 and a temperature of from 70 to 150 F., and immersing the aluminum metal for from 2 to 10 minutes in an aqueous solution of from 2 to 100 grams per liter of a salt of aurintricarboxylic acid selected from the group consisting of the sodium, potassium and ammonium salts having a pH of from 3 to 8 anda temperature from 120 to 185 F.

8. The method of claim 7 wherein the metal M in the general formula MX is chromium.

9. The method of claim 7 wherein the metal M in the general formula MX is copper.

10. The method of claim 7 wherein the metal M in the general formula MX is cobalt.

11. The method of claim 7 wherein the anion X in the general formula MX is a sulfate.

12. The method of claim 7 wherein the anion X in the general formula MX is an acetate.

13. The method of claim 7 wherein the anion X in the general formula MX is a chloride.

14. The method of claim 7 wherein the anion X in the general formula MX is a nitrate.

15. The method of claim 7 wherein the salt of aurin: tricarboxylic acid is the ammonium salt.

16. The method of claim 7 wherein the salt of aurintricarboxylic acid is the sodium salt.

17. The method of claim 7 wherein the salt of aurintricarboxylic acid is the poassium salt.

18. In the art of coloring anodic oxide coatings on aluminum metal, the improvement comprising the steps of immersing the oxide coated aluminum metal for from 2 to 7 minutes in an aqueous solution of a salt having the general formula MX, wherein M is a metal selected from the group consisting of chromium, copper and cobalt and X is an anion selected from the group consisting of sulfates, acetates, chlorides and nitrates, the concentration of said salt ranging from 1 gram of salt per liter of water to saturation, said solution having a pH of from I to 4 and a temperature from 120 to 160 F., followed by immersion for from 15 seconds to 5 minutes in an aqueous solution of from .05 to .5% by weight sulfuric acid having a pH of from 1 to 3 and a temperature of from 70 to 150 F., and immersing the aluminum metal for from 2 to 10 minutes in an aqueous solution of from 2 to grams per liter of a salt of aurint-ricarboxylic acid selected from the group consisting of the sodium, potassium, and ammonium salts maintained at a pH of from 3 to 8 and a temperature from to 185 F.

19. In the art of coloring anodic oxide coating v on aluminum metal, the improvement comprising the steps of immersing the oxide coated aluminum metal for from 5 seconds to 2 minutes in an aqueous solution of from 2 to 100 grams per liter of a salt of aurintricarboxylic acid selected from the group consisting of the sodium, potassium and ammonium salts having a pH of from 3 to 8 and a temperature of from 120 to 185 F., followed by immersion of the aluminum metal for from 15 seconds to 5 minutes in an aqueous solution of from .05 to .5 by weight sulfuric acid having a pH of from 1 to 3 and a temperature of from 70 to F., and immersing the aluminum metal for from 2 to 10* minutes in an aqueous solution of from 2 to 100 grams per liter of a salt of aurintricarboxylic acid selected from the group consisting of the sodium, potassium and ammonium salt's having a pH of from 3 to 8 and a temperature of from 120 to F.

20. In the art of coloring anodic oxide coatings on aluminum metal, the improvement comprising the steps of immersing the oxide coated aluminum metal for from 5 seconds to 2 minutes in an aqueous solution of from 2 to 100 grams per liter of a salt of aurintricarboxylic acid selected from the group consisting of the sodium, potassium and ammonium salts having a pH of from 3 to 8 and a temperature of from 120 to 185 F., immersing the so-treated aluminum metal for from 2 to 7 minutes in an aqueous solution of a salt having the general formula MX, wherein M is a metal selected from the group consisting of chromium, copper and cobalt and X is an anion selected from the group consisting of sulfates, acetates, chlorides and nitrates, said salt being in a concentration ranging from 1 gram of salt per liter of water to saturation having a pH of from 1 to 4 and a temperature from 120 to 160 F., and immersing the aluminum metal for from 2 to 10 minutes in an aqueous solution of from 2 to 100 grams per liter of a salt of aurintricarboxylic acid selected from the group consisting of the sodium, potassium and ammonium salts having a pH of from 3 to 8 and a temperature from 120 to 185 F.

21. In the art of coloring anodic oXide coatings on aluminum metal, the improvement comprising the steps of immersing the oxide coated aluminum metal for about 10 seconds in an aqueous solution containing about 25 grams per liter of ammonium bifluoride, 15 milliliters per liter of 70% nitric acid, balance water, followed by immersion of said aluminum metal for from 5 seconds to 2 minutes in an aqueous solution of from 2 to 100 grams per liter of a salt of aurintricarboxylic acid selected from the group consisting of the sodium, potassium and ammonium salts having a pH of from 3 to 8 and a temperature of from 120 to 185 F., immersing the so-treated aluminum metal from from 2 to 7 minutes in an aqueous solution of a salt having the general formula MX, wherein M is a metal selected from the group consisting of chromium, copper and cobalt and X is an anion selected from the group consisting of sulfates, acetates, chlorides and nitrates, said salt being in a concentration ranging from 1 gram of salt per liter of water to saturation, having a pH of from 1 to 4 and a temperature from 120 to 160 F., followed by immersion of the aluminum metal for 15 seconds to 5 minutes in an aqueous solution of from .05 to .5 by weight sulfuric acid having a pH of from 1 to 3 and a temperature of from 70 to 150 F., and immersing the aluminum metal from from 2 to 10 minutes in an aqueous solution of from 2 to 100 grams per liter of a salt of aurintricarboxylic acid selected from the group consisting of the sodium, potassium, and ammonium salts having a pH of from 3 to 8 and a temperature from to F.

22. A composite article comprising a base portion of aluminum metal and a red colored anodic oxide coating adhering thereto characterized by a pleasing appearance and superior light fastless produced by immersing an oxide coated aluminum article in an aqueous solution of a salt of aurintricarboxylic acid, selected from the group consisting of the sodium, potassium and ammonium salts followed by immersing the so-treated aluminum metal in an aqueous solution of a salt having the general formula MX wherein M is a metal selected from the group consisting of chromium, copper and cobalt, and X is an anion selected from the group consisting of sulfates, acetates, chlorides and nitrates, followed by immersion in an aqueous solution of sulfuric acid, and finally immersing the article for a second time in an aqueous solution of a salt of aurintricarboxylic acid selected from the group consisting of the sodium, potassium and ammonium salts.

References Cited in the file of this patent UNITED STATES PATENTS 1,946,148 Tosterud Feb. 3, 1934 2,071,156 Baer Feb. 16, 1937 2,538,317 Mason et al. Jan. 16, 1951 2,538,831 Cutter Jan. 23, 1951 FOREIGN PATENTS 387,806 Great Britain Feb. 16, 1933 OTHER REFERENCES Lederer et al.: Chromatography, second edition, page 232.

UNITED STATES PATENT OFFICE CERTIFICATE 01F @QRRECTION Patent No. 3,057J6l October 9 1962 Henry J, Wittrock It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 2, line 60 for rised read rinsed column 3,, line 3'7 for "immsersed" read immersed column 6, line 23 for "poassium" read potassium column 7 line 35 for "'metal from from" read metal 01? from column 8, line 8, for "'fastless" read 'fastness g I Signed and sealed this 21st day of May 1963,

(SEAL) Attest:

ERNEST w. SWIDER DAVID A Attesting Officer Commissioner of Patents 

1. IN THE ART OF COLORING OXIDE COATINGS ON ALUMINUM METAL, THE IMPROVEMEMT COMPRISING THE STEPS OF IMMERSING THE OXIDE COATED ALUMINUM METAL IN AN AQUEOUS SOLUTION OF A SALT OF AURINTRICARBOXYLIC ACID SELECTED FROM THE GROUP CONSISTING OF THE SODIUM, POTASSIUM AND AMMONIUM SALTS, IMMERSING THE SO-TREATED ALUMINUM METAL IN AN AQUEOUS SOLUTION OF A SALT HAVING THE GENERAL FORMULA MX, WHEREIN M IS A METAL SELECTED FROM THE GROUP CONSISTING OF CHROMIUM, COPPER AND COBALT, AND X IS AN ANION SELECTED FROM THE GROUP CONSISTING OF SULFATAED, ACETATES, CHLORIDES AND NITRATES, FOLLOWED BY IMMERSION IN AN AQUEOUS SOLUTION OF SULFURIC ACID, AND IMMERSING THE ALUMINUM METAL FOR A SECOND TIME IN AN AQUEOUS SOLUTION OF A SALT OF AURINTRICARBOXYLIC ACID SELECTED FROM THE GROUP CONSISTING OF THE SODIUM, POTASSIUM AND AMMONIUM SALTS. 